In 1900, a German scientist named Max Planck wrote an equation to show this the relationship between energy and frequency of electromagnetic radiation :

E = hn

where E is the energy of a bit of light called a quantum, A quantum is the smallest bit of electromagnetic radiation that can be emitted.It is also called a photon of light or small “packet” of electromagnetic radiation.The “h” in the above equation is a very small constant called “Planck’s constant” (6.626068 × 10^{-34} J s) and “n” is the frequency of the radiation.Through various experiments of Planck and Albert Einstein, it came to be accepted that light has properties of particles as well as waves.Planck’s “quantum” idea became the basis for the modern understanding of atomic structure.In the above equation, as the frequency of radiation increases, its energy increases by the increment “h”.In other words, energy was not continuous, it was quantized – only certain energies are allowed.Continuous energy and quantized energy can be likened to aramp versus a set of stairs connecting two levels of a building.The ramp is analogous to continuous energy – you can sit at any position along the ramp and thus be at any elevation between the two levels.The stairs are analogous to quantized or discrete energy – you can only sit at certain elevations between the two levels and nowhere in between.You may sit only on the steps, not in between the steps.Only certain elevations are allowed.